geothermal resource potential of the safford-san simon basin, arizona

Geophysics, 1979).
Nearby at Safford, the Southern Pacific well bottomed
at 555 meters in gypsiferous sediment.
Another nearby deep test well, D-7-
26-26ABA, bottomed in halite and mudstone at 689 meters. These well data
indicate that a potential geothermal reservoir at Safford is deep, possibly
between 800 meters and 1 kilometer.
Temperatures between 55 and 70 0 C are
o
possible, based upon an indicated temperature gradient of 45 C/km.
Geothermometry
Application of chemical geothermometry on these waters is not appropriate
within the qualifying assumptions required for their use (Fournier
and others, 1974).
Because these waters are probably in contact with highly
soluble evaporite minerals, the Na-K-Ca geothermometer estimates are not
believed to reflect deep reservoir conditions.
with a1pha-cristobalite at Indian Hot Springs.
Silica is in equilibrium
Silica concentrations in the
Mount Graham Mineral Bath well are super-saturated with respect to all solid
species of silica except amorphous silica (opal).
Alpha-cristobalite geothermometers
of the Mount Graham Mineral Bath well are 56°C to 64°C.
Conclusion
The thermal regime of the Gila Valley is believed generally conductive,
with systematic temperature increases with depth except near fault zones.
The heat source for the thermal waters is easily explained by the normal
flow of heat from the earth's interior in the region.
The relatively high
temperature gradients (>40 o C/km)
in this area are probably due to the insulating
affect of low heat-conductive, basin-filling sediments.
Figure 8 is a map of subsurface resistivity obtained by dipole-dipole
profiling. This map is useful to show the subsurface extent of gypsiferous
clay and evaporite minerals.
Wells drilled in the zone of low resistivity
are likely to encounter water whose TDS exceeds 3,000 mg/l.
Localized
35